This invention relates generally to apparatus for applying a tensile force to a band of fibrous tissue, such as a tendon or ligament of a patient, during surgery.
Surgeons move and/or change the length of tendons, ligaments and other bands of fibrous tissue associated with various joints of the body for many reasons. When surgeons perform these procedures, the specific tension in the band of fibrous tissue affects the outcome of the surgery.
For example, children with cerebral palsy (CP) commonly have an orthopedic problem known as equinus deformity in which their toes, rather than their heels, touch the ground at the beginning of each step. Heel cord transfer (HCT) surgery is used to correct or reduce this problem. During HCT surgery, the tendo achillis (i.e., the Achilles tendon) is removed from its insertion site on the calcaneum (i.e., the os calcis or heel bone) and repositioned at a location closer to the axis of the ankle joint. The surgery decreases the torque generating capacity of the gastrocnemius and soleus muscles (i.e., the calf muscles), thereby reducing the equinus position.
Two variables dictate the outcome of HCT surgery. The first is the position of the ankle when reattaching the tendon. The second is the tension in the tendon when it is reattached. For instance, if the foot is dorsiflexed (i.e., rotated upward) too much and/or too little tension is placed on the tendon as it is attached, then the patient may be unable to produce adequate plantarflexion torque (i.e., torque causing downward rotation of the foot). Although inadequate plantarflexion torque eliminates the equinus deformity, it also reduces the ability to push off the ground with the toes during the propulsive phase of gait, resulting in increased energy expenditure, slower gait speed, crouched gait and/or knee hyperextension.
Presently, tendon (and ligament) tension during HCT and other tendon and ligament transfers is based solely upon the experience of the surgeon and can vary widely. The resulting variation can lead to inconsistent results and can detrimentally affect the outcome of the surgery. In spite of the need for consistent results, the inventors are unaware of any clinical instruments for simultaneously setting and measuring tension in tendons and ligaments, and for periodically adjusting tension in tendons and ligaments. Further, because no instruments are used, few if any quantitative data have been recorded to evaluate the magnitudes, sensitivity, repeatability, and effectiveness of tendon and ligament transfer procedures.